Liquid drain cleaners are widely used to clean stopped drains by dissolving or softening common clogging materials as well as generating heat in the clogged material.
The most commonly used liquid drain cleaners are strongly alkaline aqueous solutions of sodium or potassium hydroxide. For drains which are particularly difficult to clear, concentrated sulfuric acid may be used.
There are hazards in the handling of drain cleaner liquids, and particularly in the handling of concentrated sulfuric acid which is highly caustic and corrosive to skin and other tissues.
The packaging of sulfuric acid drain cleaners in "unbreakable" bottles made of a resilient corrosion resistant plastic material, such as polyethylene, reduces the hazards associated with accidental breakage, but other hazards remain.
When an unstoppered bottle of concentrated sulfuric acid is dropped, or set down hard, on a horizontal surface, such as a table, tiny droplets of the acid may rise from the surface of the liquid and may thereafter come into contact with the skin or eyes of the handler. Contact with the eyes can be particularly harmful.
In addition, the accidental tipping of a bottle of concentrated sulfuric acid can be harmful to the table top or other surfaces on which the bottle is resting, even if the bottle is quickly set upright.
There is also a potential hazard in the use of caustic drain cleaners, particularly sulfuric acid drain cleaners, by reason of localized overheating which may lead to boiling. Although sulfuric acid is miscible with water, it tends to remain separate, by reason of its much higher density, and to sink to the bottom of a clogged drain to the extent permitted by the stoppage therein. In this position, there is a considerable amount of heat developed at the interface between the sulfuric acid layer and the water layer; and localized boiling may occur causing acid-containing water to emerge as droplets from the liquid-air interface. If the user is nearby to observe the operation of the drain cleaner, he may possibly be spattered by erupting acid-containing water.